Their "gold" Al-Oxide paper prices out at $0.015 per square inch, or about triple the cost of non-PSA sheets. It isn't much more of a deal than 3M 216U.
The F-weight Alumina-Zirconia stuff looks really interesting though. That's the same abrasive family as the Norzon belts that many people recommend for heavy lapping work, but with PSA and paper instead of cloth (which may improve flatness). I think I'll order some...
EDIT: Whoever set up their web storefront was laughably incompetent. I particularly like the way it clears all of your information (name, address, payment, etc) every time you adjust order quantities.